The present invention relates to a semiconductor device having oxide dielectrics, and also relates to a method of fabricating the semiconductor device.
A memory device incorporating a related ferroelectric condenser is known in the field of semiconductor devices having oxide dielectrics. This related ferroelectric condenser is composed such that a ferroelectric, which is a type of oxide dielectric, is interposed between an upper and a lower electrode. FIGS. 7A to 8B are cross-sectional views showing a related method of fabricating the related ferroelectric condenser used in the above-described memory device.
During fabrication of the related ferroelectric condenser, as shown in FIG. 7A, an insulating film 4 is formed on a substrate 2 having CMOS and other elements (not shown). A platinum layer 6 is then formed by depositing platinum on the insulating film 4 by means of sputtering. In the same manner, as shown in FIGS. 7B to 7C, a ferroelectric layer 8 and then a platinum layer 10 are formed on the platinum layer 6.
Next, as shown in FIG. 8A, an upper electrode 12 is formed by conducting RIE (Reactive Ion Etching) on the platinum layer 10, using a resist as a mask. In the same manner, as shown in FIGS. 8B to 8C, etching is successively conducted on the ferroelectric layer 8 and the platinum layer 6 using another resist (not shown) as a mask, so that a ferroelectric section 14 and a lower electrode 16 can be formed. Finally, an insulating film (not shown) is formed to cover the substrate 2.
However, problems associated with RIE etching may be encountered during fabrication of the related ferroelectric condenser. That is, the ferroelectric section 14 is formed by conducting RIE etching on the deposited ferroelectric layer 8. The RIE etching causes ions to shock the ferroelectric section 14, resulting in the ferroelectric section 14 having a tendency to develop a lattice defect. There is also a tendency for the RIE etching to cause a reducing reaction in the ferroelectric section 14. Accordingly, ferroelectricity, which is a function of the ferroelectric section 14, tends to deteriorate. These problems are especially serious in the case of a highly integrated memory device in which the area of the ferroelectric section 14 is small.
It is an object of the present invention to overcome the above-described problems by providing a semiconductor device characterized in that an operation of the oxide dielectric section (e.g., a ferroelectric) is seldom deteriorated. It is a further object of the present invention to provide a method of fabricating the semiconductor device.
In the related method of fabricating the related ferroelectric condenser, the following problems may be encountered. In order to prevent a product of etching (i.e., a side wall polymer), which is difficult to be removed, from adhering to a side 14a of the ferroelectric section 14 when RIE etching is conducted on the ferroelectric layer 8, a ratio of isotropic etching is set at a high value. Accordingly, the side face 14a of the ferroelectric section 14 is greatly inclined. This inclination results in the area required for the ferroelectric section 14 to be unnecessarily increased, which in turn obstructs the enhancement of the degree of integration of the semiconductor device into which the ferroelectric condenser is incorporated.
Further, when consideration is given to the fluctuation of the etching condition, it is necessary to provide a large margin between the ferroelectric section 14 and the upper electrode 12, or between the ferroelectric section 14 and the lower electrode 16.
It is another object of the present invention to solve the above problems by providing a semiconductor device having a degree of integration that can be easily enhanced. It is a further object of the present invention to provide a method of fabricating such a semiconductor device.
In the first aspect of the present invention, there is provided a method of fabricating a semiconductor device comprising the steps of: forming an insulating layer on a semiconductor substrate including a first layer; forming a through hole in the insulating layer so as to reach for the first layer; charging an oxide dielectric substance into the through hole to form an oxide dielectric section therein; and forming a second layer on the oxide dielectric section.
When an oxide dielectric substance is charged into the through hole, the oxide dielectric section, having the same shape as the internal shape of the through hole, is formed. Thus, the oxide dielectric section can be formed into a predetermined shape without etching. It is therefore possible to avoid the occurrence of a lattice defect and a reducing reaction, which are caused by etching the oxide dielectric section. As a result, the function of the oxide dielectric section is seldom deteriorated.
When the shape of the through hole is determined, the shape of the oxide dielectric section is thus determined. Accordingly, as compared with a case in which the shape of the oxide dielectric section is determined by etching, fluctuation of the shape of the oxide dielectric section is reduced. Therefore, it is possible to reduce a margin for absorbing the fluctuation and enhance a grade of integration of the device.
When the shape of the through hole is determined, a contact area between the first layer and the oxide dielectric section is thus determined. Accordingly, fluctuation of the contact area is reduced. In case it is constituted a condenser wherein the first layer serves as a lower electrode, capacity fluctuation thereof can be reduced.
In this connection, a method of forming the through hole in the insulating layer is not particularly restricted. For example, even when the well-known etching method is applied, the through hole can be formed with sufficiently high accuracy.
In the second aspect of the present invention, the method further comprises forming the first layer on an upper surface of the semiconductor substrate.
In the third aspect of the present invention the step of forming the oxide dielectric section includes the steps of laminating the oxide dielectric substance onto the insulating layer while filling the through hole therewith and removing the oxide dielectric substance located areas other than the inside of the through hole.
For example, the step of laminating the oxide dielectric substance is conducted by the sol-gel method and the step of removing the substance is conducted by the CMP (chemical mechanical polishing) method. Accordingly, the oxide dielectric section can be formed with significant ease.
In the fourth aspect of the present invention, the method further comprises the step of patterning the first layer before the step of forming the insulating layer.
Accordingly, in a process in which a layer arranged above the first layer (e.g., the second layer) is patterned by the etching, it is not necessary to conduct a patterning of the first layer lying in the lowermost. That is, in the above step of patterning, it is not necessary to etch deeply. Therefore, irregularities on the upper surface of the device are not so remarkable and can be flattened thereby.
In the fifth aspect of the present invention, the method further comprises the step of planarizing an upper surface of the insulating layer before the step of filling the through hole with the oxide dielectric substance.
Accordingly, when the oxide dielectric substance placed outside of the through hole is removed by, for example, the CMP method, the oxide dielectric substance can be easily and positively removed therefrom.
In the sixth aspect of the present invention, the method further comprises the step of patterning the first layer after the dielectric oxide dielectric section is formed.
Accordingly, in the step of forming the oxide dielectric section, the first layer has not been patterned yet, and the insulating layer formed on the first layer is flat. Therefore, when the oxide dielectric substrate placed outside of the through hole is removed by, for example, the CMP method, the oxide dielectric substance can be easily and positively removed therefrom.
In the seventh aspect of the present invention, the method further comprises the step of patterning the second layer so as to cover entire upper surface of the oxide dielectric substance.
Accordingly, even when the patterning is conducted by the etching, the oxide dielectric section is not affected by the etching. It is therefore possible to avoid the occurrence of a lattice defect and a reducing reaction, which are caused by the patterning of the second layer. As a result, the function of the oxide dielectric section is seldom deteriorated.
When the shape of the through hole is determined, a contact area between the second layer and the oxide dielectric section is thus determined. Accordingly, fluctuation of the contact area is reduced. In case it is constituted a condenser wherein the second layer serves as an upper electrode, capacity fluctuation thereof can be reduced.
In the eighth aspect of the present invention, an inner circumferencial wall of the through hole and the insulating layer make an angle of 80-90 degree.
Accordingly, in case it is constituted a condenser wherein the first layer serves as a lower electrode and the second layer serves as an upper electrode, such condenser having a predetermined capacity can be realized with a minimum projected plan area.
In the ninth aspect of the present invention, the step of forming the first layer includes the step of forming a first electrode on the upper surface of the semiconductor substrate in which a circuit element is formed.
In the tenth aspect of the present invention, the first layer is an impurity diffusion area formed on the upper surface of the semiconductor substrate.
Accordingly, a condenser having high reliability can be formed on the semiconductor substrate in which any desired circuit element is formed.
Further, since it is not necessary to conduct a patterning of the oxide dielectric substrate, deterioration of any circuit element arranged in lower layer can be reduced. Particularly, in case the first layer is an impurity diffusion area such as a drain or a source of a transistor, such deterioration of any circuit element arranged in the lower layer is reduced.
In the eleventh aspect of the present invention, the first layer includes a platinum layer.
In the twelfth aspect of the present invention, the first layer includes an iridium layer.
In the thirteenth aspect of the present invention, the first layer is two-layers film constituted by a lower layer made of platinum and an upper layer made of IrO2.
In the fourteenth aspect of the present invention, the step of forming the through hole is conducted by RIE.
Accordingly, the through hole, the inner circumferencial wall of which is perpendicular to the first layer, can be easily formed with high accuracy.
In the fifteenth aspect of the present invention, the step of planarizing the upper surface of the insulating layer includes the steps of forming a SOG layer so as to fill recesses formed on the upper surface of the insulating layer by the SOG method and etching back an upper portion thereof.
In the sixteenth aspect of the present invention, the step of laminating the oxide dielectric substance is conducted by the sol-gel method and the step of removing the substance is conducted by the etching-back.
In the seventeenth aspect of the present invention, the step of laminating the oxide dielectric substance is conducted by the sputtering method and the step of removing the substance is conducted by the CMP method.
According to any one of the fifteenth to seventeenth aspects of the present invention, an accurate condenser having less fluctuation of capacity can be easily realized without damaging any lower layer.
In the eighteenth aspect of the present invention, there is provided a semiconductor device comprising: a first layer formed on an upper surface of a semiconductor substrate; an oxide dielectric section formed on the first layer, an outer peripheral side face of which is surrounded by an insulating layer such that the outer peripheral side face and the insulating layer make an angle of 80-90 degree; and a second layer is formed on the oxide dielectric section.
Accordingly, in case it is constituted a condenser wherein the first layer serves as a lower electrode and the second layer serves as an upper electrode, such condenser having a predetermined capacity can be realized with a minimum projected plan area. As a result, a device having a high grade of integration can be realized.
In the nineteenth aspect of the present invention, the first layer is an electrode including a platinum layer, and the first and second layers sandwich the insulating layer and the oxide dielectric section therebetween.
In the twentieth aspect of the present invention, the first layer is two-layers film constituted by a lower layer made of platinum and an upper layer made of IrO2.
In the twenty-first aspect of the present invention, the oxide dielectric section is made of selected one of PZT, SBT and PLZT, and an ferroelectric condenser is constituted by the first and second layers and the oxide dielectric section.
In the twenty-second aspect of the present invention, the first layer is one of a source layer and a drain layer of a transistor, and an ferroelectric condenser is constituted by the first and second layers and the oxide dielectric section.
According to any one of the twentieth to twenty-second aspects of the present invention, a semiconductor device having high reliability and accuracy can be realized.
In this connection, hereinafter, xe2x80x9cto form the first layer on the semiconductor substratexe2x80x9d or xe2x80x9cto provide the first layer on the semiconductor substratexe2x80x9d is a concept including the following three cases. The first case is that the first layer is formed coming into contact with the semiconductor substrate. The second case is that the first layer is formed on at least one another layer such as an insulating layer, which has already been formed on the semiconductor substrate. The third case is that the semiconductor substrate itself if the first layer.